The invention relates to a system for attaching a structural member to a supporting member.
There is frequently an object to safely attach a structural member to a supporting member and to arrange for the structural member not to come off by itself because of a permanent vibration of the supporting member. In addition, there is an object to mount the structural member on the supporting member in a sealed and vibration-cushioned way. Such a case exists, for example, when a hood is attached which requires to be fixed to the engine block as a cover of the cylinder head. A similar attachment case also exists when intake pipe systems are mounted. The supporting member mostly has mounted thereon so-called studs to which the structural member is then attached by means of a nut. However, a common nut when being tightened only has a small angle of rotation of 360xc2x0, for example, to apply the torque required. The risk is that the nut will loosen after some time. In such a xe2x80x9cseverexe2x80x9d thread-on case, merely a slight distortion of the nut already causes it to be loosened, which is undesirable. The nut might also be loosened by the fact that the entire assembly undergoes permanent deformation, which is also called a setting deformation, because of the tension and compression forces which are applied. A slight stress relief already causes the bias to be eliminated.
It is the object of the invention to provide a system for attaching a structural member to a supporting member wherein the attached assembly is prevented from getting independently loosened despite the setting deformation phenomena.
The object is attained by the features of the instant invention.
The inventive system consists of three components, i.e. a sleeve, a nut arrangement, and an annular sealing element. However, it should be noted that the annular sealing element, which is preferably made of an elastomeric material, may be omitted if neither a sealing effect nor any cushioning of vibrations is desired.
The sleeve has a radial flange and has an inner diameter which is slightly larger than the outer diameter of the stud. The nut arrangement has a nut portion which is adapted to be threaded onto the stud. It further has a fastening portion which is adapted to be captivated to the flange of the sleeve, in which case, however, a relative rotation is possible between the sleeve and the nut arrangement. An elastically deformable portion is provided between the nut portion and the fastening portion, which yields if the nut arrangement, while being axially pressed against the sleeve, is threaded onto the stud. At this stage, the fastening portion of the nut arrangement will come into engagement with the radial flange of the sleeve which, in turn, is supported on the supporting member or on an abutment surface of the stud of the supporting member. At the same time, the structural member to be attached is pressed against the supporting member via the radial flange of the sleeve.
The nut arrangement is made of steel, preferably spring steel, which is rather strong although it makes possible a certain axial deformation in the deformable portion. In this way, a rotation through 360xc2x0 may take place twice or three times while the nut portion is tightened. This causes a bias to be built up via a relatively large path, which will not get lost either even if the nut arrangement loosens by a certain angle of rotation, for example, or setting deformation phenomena are encountered.
The nut arrangement is of a large hardness which is achieved in a multi-stage quench-and-temper procedure. Such a procedure is known as such. The aim is to achieve a hardness of from 45 to 50 HRC (Rockwell hardness) for the inventive nut arrangement.
According to an aspect of the invention, the outer side of the nut arrangement has formed thereon wrench surfaces, preferably in the shape of a hexagon. The wrench surfaces are preferably located in a portion larger in diameter between the nut portion and the fastening portion. As a result, the nut arrangement allows to use wrenches of larger dimensions, which makes it easier to apply a high torque.
In another aspect of the invention, a provision is made for the nut arrangement to have the shape of a stepped sleeve with the exception of the fastening portion, with the nut portion having a first outer diameter and the joining portion having a second outer diameter and the rounded step between the portions forming the deformable portion. The step or shoulder is of a slightly conical shape with appropriately rounded transition zones being provided towards the fastening portion and nut portion so as to avoid inadmissible stresses on the material during deformation.
According to another aspect of the invention, the fastening portion has a flange which engages the flange of the sleeve, and at least two hook-shaped gripping portions are formed to the circumference of the radial flange which engage the edge of the sleeve flange. It is imaginable to produce the captive, but rotatable connection between the nut arrangement and the sleeve in another way, particularly if sufficient space is available. Forming hook-shaped gripping portions saves exceptionally much space and is completely sufficient to provide the captive nature. Particular forces need not be transmitted in this region. Preferably, three gripping portions are provided which are offset by 120xc2x0 from each other.
In another aspect of the invention, the other end of the sleeve also has formed thereto a radial flange which preferably extends outwardly. It will then bear against the supporting member or a bearing contact surface of the stud. In this manner, the sleeve acts as a spacer and prevents the sealing element from being subjected to too large a compression. Furthermore, the rotatability between the nut arrangement and the sleeve prevents the sealing element from undergoing a torsion while the nut arrangement is tightened.
As was previously mentioned the sleeve can be supported on an abutment surface of the stud. The abutment surface may be formed by an enlarged portion of the stud which has wrench surfaces at its circumference. For example, the stud is screwed into appropriate threaded bores in engine blocks. The wrench surfaces may then be used to apply an appropriate torque with a view to efficiently attaching the stud to the engine block.